This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The Olive View Medical center has a high throughput breast clinic that serves a large area in Los Angeles. If Diffuse Optical Spectroscopy is to be a useful technology, several important questions must be addressed: (1) Is the DOS instrument robust enough to be used in a high traffic clinic? (2) Can non-optics personnel be easily trained to use the DOS instrument? (3) How does DOS correlate with mammographic breast density? (4) Can DOS see tumors in patients with high mammographic breast density? (5) Can DOS see tumors that are deep within the breast?